Members of the cyclin-dependent kinase (CDK) family are believed to play important roles in regulating cellular proliferation. The predominant target of the inhibitors described herein, CDK7, exists as a heterotrimeric complex in the cytosol and also forms the kinase core of the RNA polymerase (RNAP) II general transcription factor complex in the nucleus. Within that complex, CDK7 phosphorylates the C-terminal domain (CTD) of RNAP II, which is a requisite step in initiating gene transcription.